Category Archives: Fără categorie

Enhancing the dynamic frequency of microgrids by means of PV power plants with integrated energy storage

Fără categorie

Abstract

Achieving a high-level of stability represents one major concern in autonomous microgrids (MGs) with high penetration levels of renewable energy sources. The aim of this paper is to study how photovoltaic (PV) power plants can provide dynamic frequency support in MGs, in order to obtain an improved stability for the entire power system. On the PV side an energy storage subsystem is added, with the main purpose of better control and higher power reserve of the PV power plant. By this way the necessary input power is provided by the PV system along with the battery block. The required output power is supplied by a three-phase voltage source converter (VSC). The VSC control is implemented in a rotating dq reference frame, including a harmonic compensation loop for the output current. To improve the dynamic frequency stability of the MG, specific functions are implemented within the PV inverter control. To highlight the performance of the proposed system, a comparative analysis is provided, which cover four cases of interest depending on the status of the storage system and dynamic support (i.e. with/without storage and with/without dynamic support). Simulation results are included to validate the power control system, showing that the dynamic frequency control can be improved by the proposed solution. images

Dynamic Regime Electromagnetic Torque in Brushless Direct Current Motors

Fără categorie

Abstract

This study aimed at establishing the mathematical model for determining the dynamic regime torque and at emphasizing constructive aspects which influence its magnitude and variation. Brushless direct current motors are very present and there have been carried out researches regarding their design and optimum construction. The technology evolution in several areas has caused an increase in production of permanent-magnet BLDC motors, which has good technical-economic performances for a large range of controlled-speed applications. The study carried out, by the simulations we presented, shows that these motors have high torque oscillations in a complete rotation. There are identified the slots which create high torques, respectively low torques, in a complete rotation, thus justifying the oscillations. In this paper there is emphasized that the optimum variant of maximum torque involves a supply by six pulses per period in direct direction, also indicating the value of the control angle. The most unfavourable variant occurs at brushless direct current motor supplied by three pulses per period and reverse succession of phases, where the average value of the torque decreases by 56.7% over the optimum machine. A complete elimination of oscillations in this type of motor is not possible, but an optimal design can reduce them considerably images

Small Scale Model of Automatic Barrier Powered by Photovoltaic Panel

Fără categorie

Abstract

Access control systems offer numerous benefits and are able to constitute extremely good solutions for securing an area of high or very high importance. An access control system allows restriction, monitoring and directing human trafficking as cars to a location or from a location. In generally at access control systems call the managers of circulated spaces or areas where must enter only authorized persons. To access the vehicles in different areas are frequently used automatic barriers. This paper presents such an access system, achieved a small scale named ˝automatic barrier model˝, that uses photovoltaic panels (PV) as main energy source. Automatic operation of barrier is provided by a development system achieved around a microcontroller. In the first part of paper is presents the structure and minimum requirements of development system. Also are highlighted aspects of dimensioning and design for both parts hardware and software respectively. To achieve electrical diagrams and PCBs was used a dedicated software. Finally was tested the achieved automatic barrier model. The tests consist of verifying the correct operation of the automated system. Were made test regarding to automation and to power supply from PV panel. Experimental results show a smooth functioning of experimental automatic barrier powered by PV panel and can be successfully expanded at real scale. images

Design and Simulation of Wireless Power Transfer Systems

Fără categorie

Abstract

This paper presents a set of diagrams for wireless power transfer systems (WPTS) with a lot of applications in key domains such as: medical, electrical engineering, military etc. Our research is based on circuits working as WPTS. All the circuits are using sets of two magnetically coupled coils whose parameters were extracted by simulations using the specialized software ANSOFT Q3D EXTRACTOR. The simulations of the circuits were performed using TINA, SPICE and SIMULINK in MATLAB. We used existing parts from Texas Instruments libraries. WPTS are more appropriate for small distances transmission, distances up to twice the coils dimensions, because the magnetic field strength produced by the transmitter becomes very weak when the distance increases. In contrast to other WPTS methods, the efficiency of the system can reach up to 95% for short distance. The circuits were also physically built and tested and the results were very close to the numerical ones. We also compared the results with data in existing literature and we obtained a bound of the error of less than 5%. We also studied the efficiency of the power transfer and presented some practical applications for these systems such as low power battery chargers. The results done by simulations were almost identical with the experimental ones and those in existing literature, the error being less than 5%. images

Modeling and Simulation of the Coal Flow Control System for the Longwall Scraper Conveyor

Fără categorie

Abstract

In this paper, the modeling and simulation of a coal flow control system for the longwall scraper conveyor is presented. The coal flow on the scraper conveyor, it is controlled by the following variables: the coal flow, advance speed and cutting speed of the longwall shearer. The electrical drive system of the longwall scraper conveyor together with the electrical drive system of the advancement and the cutting mechanism of the longwall shearer are done by means of induction motors. The control of speeds and electromagnetic torque of induction motors is realized by using sensorless vector control systems. Within these control systems, the estimation of position and of components of the rotor flux space-phasor, as well as the rotor speed of the induction motor, is done by an extended Gopinath observer. The advantages of a coal flow control system are control of productivity and also that electric motors of the flow of transport can be optimally chosen, leading ultimately to a much lower consumption of electricity for coal extraction. Modeling and simulation of control systems is done taking into account the mathematical equations that make the connection between constructive and functional parameters of the longwall shearers with the features of the strata of mining coal, specifically the coal deposits from the Jiu Valley, Romania. images

Monitoring and Analysis of the Electrical Parameters for an Industrial Consumer using LabVIEWEnvironment

Fără categorie

Abstract

 This paper presents a case study for monitoring the quality of electric energy in an industrial consumer. The measurements were carried in the power supply point where the quality of the electric energy is influenced by the activity of the manufacturer, the transmission and distribution provider, the supplier as well as the electric power consumer activity. Transients occur at this limiting point, with negative effects on the consumer, as well as on the electric power supply network. There are two types of electric energy quality indicators, depending on the point of occurrence. Primary quality indicators are given by the production, transport and distribution of electric energy. Secondary indicators are given by the disruptive operation of industrial consumers. The data processing was achieved using LabVIEW software in terms of the two types of quality indicators. Based on the data obtained from the measurements and using the interface created in LabVIEW, it was possible to carry out the analysis of the average hourly consumption, the power factor, the wave forms of the current and voltage, the analysis of the current and voltage harmonics. The software application enables creation of customized reports with varying ease of use and flexibility. Using the software application developed in LabVIEW, full quality analysis of electric energy can be done at the user’s premises. images

Simulation and Implementation of Sensorless Control Using Estimators in Electric Drives with HighDynamic

Fără categorie

Abstract

In this article we’ll tackle the control of electric drive with high dynamic, with rapid changes in torque and speed, where the control strategy is FOC (Field Oriented Control). In the surface mining industry, from which the electric drive application for this article is selected, the general trend is toward using asynchronous motors with shortcircuit rotor, due to the advantages of this motor both in terms of design and operation. In order to achieve the variable speed, must be used the static frequency converters. Simulations were carried out using a converter with FOC control strategy and a 45kW motor. The simulations also followed the direction from simple to complex in order to emphasize both qualitative and quantitative elements with respect to the overall dynamic behavior. Simulations were carried out both in the case where the overall structure contains an encoder for speed information, and where the sensorless approach is used the implementation of an estimator is strictly necessary. Such cases were dealt with where speed is measured directly with an encoder, compared with the case of sensorless control, where speed is estimated using a Model References Adaptive Control Estimator. Simulations were carried out in MATLAB/Simulink environment, highlighting the control structures and comparative results achieved for a drive application commonly used in surface mining industry. Following these directions a functional application was implemented and tested. images

Improving the Power Quality and Controllability of PV Power Plants for Microgrids Integration

Fără categorie

Abstract

This paper deals with the implementation of the control strategy for a three-phase voltage source inverter (VSI) system with the purpose of improving the power quality and controllability of photovoltaic (PV) system for microgrids (MGs) integration by means of energy storage system. The proposed model comprises of a PV power plant with an energy storage system coupled to the grid by means of a VSI. The PV system and the battery storage are integrated with the help of DC-DC and DC-AC converters in such a way that bidirectional flow of active and reactive powers can be achieved. The required power for the connected loads can be effectively delivered and supplied by the proposed PV system and energy storage systems, subject to an appropriate control method. The ultimate goal of any power system is to maintain a balance between demand and supply of active power at any set point in time. Controllers integrating energy sources respond to the received signals and attempt to fulfil the grid demand. The system response is almost instantaneous and thus can be very helpful in grid frequency and voltage support. The grid voltage harmonic generation influences the PI current controller and generates current harmonics; the used harmonic compensator is effective for both positive and negative sequence fifth and seventh harmonics. The proposed control system is validated by means of simulation results. images

Energetic Analysis of the Drying Process of Cur-rent Transformers from 110 kV Ciungetu Power Station

Fără categorie

Abstract

Currently, at company Hidroserv Râmnicu Vâlcea, the drying of current transformers used in power transformer stations is done by a combination between induction and conduction heating at the frequency of 50 Hz. Obviously, this solution is outdated in terms of technology and the performed energetic analysis proves it. In order to achieve the design of a multifunction static system intended to replace the existing one, so as to respond as best as possible to the specific needs, it is necessary to analyze the drying process from energetic point of view. The knowledge of the equivalent parameters of the loads is needed too. To substantiate the feasibility of this new technical solutions, the goal of the paper is the analysis of the actual technology from energetic point of view. Considering that the current transformer of the 110 kV power station Ciungetu is the typical load, experimental determinations relating to the its drying process have been performed. Two heating coils are used, of 33 turns and 38 turns, respectively. In order to determine the associated parameters for both coils, the current and voltage across the equivalent induc tor have been recorded by using an oscilloscope Tektronix TDS3000. It is obvious, and the performed energetic analysis demonstrates this, the solution currently used is outdated in terms of technology. images

Development of a Barrier Structure Actuated by Three Shape Memory Alloy Springs

Fără categorie

Abstract

In this paper, the authors present an experimental analysis in order to highlight the behavior of a barrier structure model, actuated by three shape memory alloy (SMA) helical springs. The authors have developed this new barrier structure to increase the performances of conventional barriers, based on SMAs unique properties and their advantages. SMAs are advantageous for actuation because of their light weight, silent operation and flexibility. SMAs began to be increasingly present in industrial applications as well because they display high reliability and can replace the functions that make the motors or complex gears despite their simple construction. The actuator used in our model works as a linear actuator, contracting itself with great strength and speed, thus exerting the necessary force to lift the barrier arm when the SMA springs are heated by carrying an electric direct current. The designer can control the direction of actuation, the amount of force generated and the stroke of the actuator through various combinations that he can achieve with these three SMA springs. After a description of the accomplished model and of how it works, the authors present an experimental analysis of the behavior displayed by the SMA springs-based barrier structure. The experiments consisted in the determination of the SMA spring functioning time periods at constant value of the SMA spring activating electric current, and while maintaining the barrier arm stroke and weight constant. images